Catalyst and process for producing aromatic nitriles

ABSTRACT

The present invention relates to a catalyst which comprises a vanadium oxide, a chromium oxide, a molybdenum oxide and a boron oxide supported on a silica carrier. This catalyst is suitable for use in the production of aromatic nitriles from alkyl-substituted aromatic compound by the catalytic reaction of a gas mixture containing an alkyl-substituted aromatic compound, ammonia and oxygen or a gas containing molecular oxygen over a catalyst. The present invention further relates to a process for producing the aromatic nitriles using said catalyst.

BACKGROUND OF THE INVENTION

This invention relates to a catalyst suitable for use in producingaromatic nitriles by catalytic reaction of a gas mixture containing analkyl-substituted aromatic compound, ammonia, and oxygen or a gascontaining molecular oxygen over such catalyst and a process forproducing aromatic nitriles using the catalyst.

DESCRIPTION OF THE PRIOR ART

Aromatic nitriles are intermediates important in organic chemicalindustry. For example, phthalonitrile is used as a starting material forproducing xylylenediamine useful as synthetic resins, agriculturalagents, and curing agents for diisocyanate or epoxy resin.

Hitherto, various processes have been proposed for producing aromaticnitriles by reacting an alkyl-substituted aromatic compound, ammonia andoxygen and Japanese Patent Publication No. 45-19284 discloses thesuperior performances of ternary catalyst composed of vanadium, chromiumand boron. Further, G.B. Patent 1351523 discloses superiority of theabove ternary catalyst which comprises a vanadium oxide, a chromiumoxide and a boron oxide at an atomic ratio of 1:(0.5-2.0):(0.1-1.2)supported in an amount of 30-60 % by weight on a silica carrier.

Vapor phase ammoxidation reactions of alkylsubstituted aromaticcompounds generate a large amount of heat of reaction. Therefore,control of reaction temperature is very difficult and fluidized bed typereactor is especially effective for the reaction. The invention of G.B.Patent 135123 which uses silica as a carrier is an improvement of theinvention of Japanese Patent Publication No. 45-19284, and the catalystof the former is used in fluidized bed reactors and exhibits excellentperformances. However, these catalysts of the prior art decrease inselectivity to the corresponding aromatic nitriles with time when usedfor a long time.

SUMMARY OF THE INVENTION

The inventor has been intensively researched to prevent the reduction ofselectivity with time. It has been found that this can be much improvedby using a fourcomponent catalyst which a molybdenum oxide is furtheradded to the ternary catalyst comprising a vanadium oxide, a chromiumoxide and boron oxide supported on silica.

Thus, the present invention provides a catalyst suitable for use in theammoxidation of alkyl-substituted aromatic compounds to aromaticnitriles which comprises a vanadium oxide, a chromium oxide, amolybdenum oxide and a boron oxide supported on a silica carrier.

The present invention also provides a process for producing an aromaticnitrile which comprises subjecting a gas mixture containing analkyl-substituted aromatic compound, ammonia and oxygen or a gascontaining molecular oxygen to pass over a catalyst which comprises avanadium oxide, a chromium oxide, a molybdenum oxide and a boron oxidesupported on a silica carrier.

DETAILED DESCRIPTION OF THE INVENTION

The atomic ratio of vanadium:chromium: molybdenum:boron which arecatalyst components of the present invention is preferably1:(0.5-2.0):(0.01-1.2) :(0.01-1.2).

As mentioned above, since the reaction of the present invention involvesvigorous generation of heat, it is advantageous to carry out thereaction in a fluidized bed or a moving bed for removal of heat ofreaction to prevent partial heating, although the characteristics of thecatalyst can be exhibited and the excellent performances can bemaintained even if the reaction is carried out in a fixed bed.

A vanadium oxide, a chromium oxide, a molybdenum oxide and a boron oxidemay be used as raw materials for the catalyst. Alternatively variouscompounds, which are readily converted to the corresponding oxides bysuitable treatment such as heating when the catalyst is prepared, may beused. These compounds include, for example, ammonium metavanadate,vanadyl sulfate and vanadium salts of organic acids such as oxalic acidand tartaric acid etc., as the vanadium raw materials; chromic acid,chromium nitrate, chromium hydroxide, ammonium chromate, ammoniumbichromate and chromium salts of organic acids such as oxalic acid andtartaric acid etc. as chromium raw materials; ammonium molybdate,ammonium paramolybdate, molybdic acid, molybdenum chloride andmolybdenum salts of organic acids such as oxalic acid and tartaric acidas molybdenum raw materials; boric acid and ammonium borate as boron rawmaterials.

As the silica which supports these catalyst components, for example,silica gel, colloidal silica and anhydrous silica which are disclosed in"Kagaku Binran (Handbook of Chemistry), Section of Applied Chemistry I",pages 256-258 (published from Maruzen Co. in 1986). Total percentage ofthe catalyst component oxides in the catalyst is 20-80% by weight,preferably 30-60 % by weight (the oxides being expressed as V₂ O₅, CR₂O₃, MoO₃ and B₂ O₃, respectively).

The present catalyst can be prepared by known methods. For example,aqueous ammonium molybdate solution and aqueous boric acid solution areadded to a solution of vanadium oxalate and chromium oxalate and then asilica sol is added thereto to obtain a slurry mixture. In this case, ifnecessary, a dissolving aid for boric acid is used. The dissolving aidfor boric acid includes polyhydric alcohols, α-monooxycarboxylic acids,and dioxycarboxylic acids.

In the case of a fluidized bed catalyst, the resulting mixture is spraydried and, if necessary, is further dried at 110-150° C. and thencalcined. In the case of a fixed bed catalyst, the mixture is evaporatedto dryness and then is calcined. Calcination is carried out at 400-700°C., preferably 450-650° C. for a few hours or more while passing air. Ifprior to this calcination a preliminary calcination is carried out at200-400° C., more favorable results can be obtained.

The alkyl-substituted aromatic compounds used as a starting material inthe present invention include, for example, toluene, ethylbenzene,polymethylbenzene (such as xylene, mesitylene, cymene, and durene),diethylbenzene and methylnaphthalene.

A suitable concentration of the alkyl-substituted aromatic compound inthe gas mixture is 0.5-5 vol % when air is used as the oxygen source.

The amount of ammonia used may be at least the theoretical amount (1 molof ammonia per 1 mol of alkyl group). The higher molar ratio ofammonia/aromatic compound in the gas mixture is advantageous forimproving yield of nitrile from the aromatic compound, but in view ofthe necessity to recover unreacted ammonia, amount of ammonia is thetheoretical amount or more, preferably about 2-10 times as much as thetheoretical amount.

Usually, air is used as oxygen source, and nitrogen, carbon dioxide orsteam can be used as an inert diluent. Amount of oxygen to be fed is atleast 1.5 times as much as the theoretical amount and preferably 2-50times as much as the theoretical amount.

Temperature of the reaction can be in a wide range of 300-500° C., butpreferably 330-470° C. When the temperature is lower than 300° C,conversion of the raw material aromatic compound is low and when higherthan 500° C., production of carbon dioxide and hydrogen cyanide isincreased, resulting in reduction in the yield of nitrile. Reactiontemperature for obtaining the maximum yield of nitrile depends on thekind of aromatic compound, concentration of raw materials, contact timeand calcination conditions for catalyst. So it is preferred tooptionally select the reaction temperature within the above rangedepending on the conditions.

Contact time of the gas mixture with the catalyst may be varied over awide range but is preferably 0.5-30 seconds.

The reaction of the present invention is usually carried out underatmospheric pressure, but can be carried out under an elevated pressureor a reduced pressure.

Collection of reaction product can be effected by any suitable methods,for example, by cooling to a temperature enough to precipitate theproduct or by washing the reaction product gas with water or othersuitable solvent.

According to the process of the present invention which comprisescarrying out the catalyst reaction of a gas mixture containing analkyl-substituted aromatic compound, ammonia and oxygen or a gascontaining molecular oxygen using a catalyst comprising a vanadiumoxide, a chromium oxide, a molybdenum oxide and a boron oxide supportedon a silica carrier thereby to produce aromatic nitriles, reduction withtime of selectivity to the corresponding aromatic nitriles is very smalland stable performance of the catalyst can be obtained for a long periodof time as shown by the following examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in more detail by the followingexamples and comparative examples.

Comparative Example 1

Preparation of catalyst

500 ml of water was added to 247 g of vanadium pentoxide, V₂ O₅,followed by heating to 80-90° C. Then, 514 g of oxalic acid, (COOH)₂ 2H₂O was gradually added with well stirring to obtain a vanadyl oxalatesolution. Separately, 400 ml of water was added to 1029 g of oxalicacid, followed by heating to 50-60° C. Then a solution of 271 g ofchromic anhydride CrO₃ in 200 ml of water was gradually added to theoxalic acid solution with well stirring to obtain a chromium oxalatesolution.

The resulting chromium oxalate solution was mixed drop-wise with theresulting vanadyl oxalate solution at 50-60° C. to prepare avanadium-chromium solution, to which 1667 g of a 30 wt % aqueous silicasol was further added.

To this slurry solution was added 84 g of boric acid H₃ BO₃, then thisslurry was well mixed and concentrated until amount of the liquidreached about 3570 g.

This catalyst solution was spray dried with an inlet gas temperature of250° C. and an outlet gas temperature of 130° C. The thus spray driedcatalyst was dried in a drier of 130° C. for 12 hours. Then, thecatalyst was preliminary calcined at 400° C. for 0.5 hour and thereaftercalcined at 550° C. for 8 hours while passing air. This catalyst had anatomic ratio V:Cr:B of 1:1:0.5 and an oxide concentration of 50 wt %.

Test for Catalyst Performance

A 40 ml of the resulting catalyst was packed in a reactor having aninner diameter of 23 mm which was heated in a molten salt bath, apreheated gas mixture consisting of 3.0 mol % of m-xylene, 21.0 mol % ofammonia and 76.0 mol % of air was contacted with the catalyst at an SVof 750 Hr⁻¹ and at 420° C. which gives the maximum yield ofisophthalonitrile. The yield of isophthalonitrile and m-tolunitrile were81.2 mol % and 2.7 mol % based on m-xylene respectively. Selectively ofthe catalyst for isophthalonitrile to the reacted m-xylene was 82.2 mol%.

By the above method, the reaction was continued for 6 months withsuitably changing the reaction temperature to the temperature at whichthe maximum yield of isophthalonitrile is obtained. The yield ofisophthalonitrile and m-tolunitrile were 75.2 mol % and 2.2 mol % basedon the m-xylene. Selectivity of the catalyst for isophthalonitrile tothe reacted m-xylene was 76.1 mol %.

EXAMPLE 1

Preparation of catalyst

A 500 ml of water was added to 242 g of vanadium pentoxide, V₂ O₅,followed by heating to 80-90° C. Then, 503 g of oxalic acid, (COOH)₂ 2H₂O was gradually added with well stirring to obtain a vanadyl oxalatesolution. Separately, 400 ml of water was added to 1016 g of oxalicacid, followed by heating to 50-60° C. Then a solution of 266 g ofchromic anhydride CrO₃ in 200 ml of water was added to the oxalatesolution with well stirring to obtain a chromium oxalate solution.

The resulting chromium oxalate solution was mixed with the resultingvanadyl oxalate solution to prepare a vanadium-chromium solution. Tothis solution were added drop-wise a solution of 47 g of ammoniumparamolybdate (NH₄)₆ Mo₇ O₂₄ 4H₂ O in 300 ml of water and furthermore,1667 g of a 30 wt % aqueous silica sol.

To this slurry solution was added 33 g of boric acid H₃ BO₃, then thisslurry was well mixed and concentrated until amount of the liquidreached about 3800 g.

This catalyst solution was spray dried with an inlet gas temperature of250° C. and an outlet gas temperature of 130° C. The thus spray driedcatalyst was dried in a drier of 130° C. for 12 hours. Then, thecatalyst was preliminary calcined at 400° C. for 0.5 hour and thereaftercalcined at 550° C. for 8 hours while passing air. This catalyst had anatomic ratio V:Cr:Mo:B of 1:1:0.1:0.2 and an oxide concentration of 50wt %.

Test for catalyst performance

In the same manner as in Comparative Example 1, the resulting catalystwas examined on activity and change of performance with time.

A gas mixture consisting of 3.0 mol % of m-xylene, 21.0 mol % of ammoniaand 76.0 mol % of air was fluid contacted with the catalyst at an SV of750 Hr⁻¹ and at 400° C. which is a temperature to give the maximum yieldof isophthalonitrile. The yield of isophthalonitrile and m-tolunitrilewere 82.7 mol % and 1.3 mol % based on the m-xylene respectively.Selectivity of the catalyst for isophthalonitrile to the reactedm-xylene was 83.5 mol %.

By the above method, the reaction was continued for 6 months withsuitably changing the reaction temperature to the temperature at whichthe maximum yield of isophthalonitrile is obtained. The yield ofisophthalonitrile and m-tolunitrile were 82.5 mol % and 1.4 mol % basedon the m-xylene respectively. Selectivity of the catalyst forisophthalonitrile to the reacted m-xylene was 83.3 mol %.

EXAMPLE 2

A catalyst having an atomic ratio of V:Cr:Mo: B=1:1:0.3:0.5 was preparedin the same manner as in Example 1 and activity and change ofperformance with time of this catalyst were examined.

A gas mixture consisting of 3.0 mol % of m-xylene, 21.0 % of ammonia and76.0 % of air was contacted with this catalyst at an SV of 750 Hr⁻¹ andat 420° C. which is a temperature to give the maximum yield ofisophthalonitrile. The yield of isophthalonitrile and m-tolunitrile were79.8 mol % and 2.2 mol % based on m-xylene, respectively. Selectivity ofthe catalyst for isophthalonitrile to the reacted m-xylene was 80.5 mol%.

By the above method, the reaction was continued for 6 months withsuitably changing the reaction temperature to the temperature at whichthe maximum yield of isophthalonitrile is obtained under the sameconditions. The yield of isophthalonitrile and m-tolunitrile were 79.8mol % and 2.3 mol % based on the m-xylene respectively. Selectivity ofthe catalyst for isophthalonitrile to the reacted m-xylene was 80.4 mol%.

EXAMPLE 3

A catalyst prepared in Example 1 was tested on activity and examined onchange of performance with time in the same manner as in Example 1except that p-xylene was used in place of m-xylene.

A gas mixture consisting of 3.1 mol % of p-xylene, 19.9 mol % of ammoniaand 77.0 mol % of air was contacted with this catalyst at an SV of 800Hr⁻¹ and at 400° C. which is a temperature to give the maximum yield ofthe phthalonitrile. The yield of terephthalonitrile and p-nitrile were83.5 mol % and 2.5 mol % based on p-xylene, respectively. Selectivity ofthe catalyst for terephthalonitrile to the reacted p-xylene was 84.0 mol%.

By the above method the reaction was continued for 6 months withsuitably changing the reaction temperature to the temperature at whichthe maximum yield of terephthalonitrile is obtained under the sameconditions. The yield of terephthalonitrile and p-nitrile were 83.1 mol% and 2.3 mol % based on the p-xylene respectively. Selectivity of thecatalyst for terephthalonitrile to the reacted p-xylene was 83.9 mol %.

EXAMPLE 4

The catalyst prepared in Example 1 was tested on activity and examinedon change of performance with time in the same manner as in Example 1except that toluene was used in place of m-xylene.

A gas mixture consisting of 5.1 % of toluene, 25.0 % of ammonia and 69.9% of air was contacted with this catalyst at an SV of 840 Hr⁻¹ and at410° C. which is a temperature to give the maximum yield ofbenzonitrile. The yield of benzonitrile was 83.3 mol % based on toluene.Selectivity of the catalyst for benzonitrile to the reacted toluene was84.3 mol %.

By the above method, the reaction was continued for 6 months withsuitably changing the reaction temperature to the temperature at whichthe maximum yield of benzonitrile is obtained under the same conditions.The yield of benzonitrile was 83.0 mol % based on the toluene.Selectivity of the catalyst for benzonitrile to the reacted toluene was83.8 mol %.

What is claimed is:
 1. A process for producing an aromatic nitrilecomprising subjecting a gas mixture containing 0.5-5 % by volume of analkyl-substituted aromatic compound selected from the group consistingof toluene, ethylbenzene, xylene, mesitylene, cymene, durene,diethylbenzene or methylnaphthalene, ammonia and oxygen or a gascontaining molecular oxygen, to a catalytic reaction, at a reactiontemperature of 300°- 500° C. for a contact time of 0.5-30 seconds,wherein the catalyst consists essentially of vanadium oxide, chromiumoxide, molybdenum oxide and boron oxide in an atomic ratio of V:Cr:Mo:Bof 1:0.5-2.0:0.01-1.2:0.01-1.2 and is supported 20-80 % by weight on asilica carrier.
 2. A process according to claim 1 wherein the gasmixture contains ammonia in an amount not less than the theoreticalamount.
 3. A process according to claim 1 wherein the gas containingmolecular oxygen is air.
 4. A process according to claim 1 wherein theamount of oxygen present in the gas mixture is at least 1.5 times thetheoretical amount.
 5. A process according to claim 1 wherein the gasmixture containing an alkyl-substituted aromatic compound, ammonia andoxygen or a gas containing molecular oxygen is subjected to catalyticreaction with the catalyst in fluidized state.
 6. A process according toclaim 3 wherein the gas mixture contains 0.5-5 % by volume of thealkyl-substituted aromatic compound.